Method of making arsenical salts



"WILLIAM THUM, 0F HAMMOND, AND JOHN J. MULLIG'AN, OF EAST CHICAGO, INDI-ANA, AND HENRY M SCHLEICHER, OF BOSTON, MASSACHUSETTS, ASSIGNORS TOUNITED STATES SMEL'IING, REFINING- &. MINING COMPANY, A CORPORATION OFMAINE.

METHOD OF MAKING ARSENICAL SALTS.

No Drawing.

T 0 all whom it may concern:

Be it known that we, (1) \ViLL AM T HUN, (2) JOHN-J. MCLLIGAN, and (3)HENRY M. SoHLmoi-Iun, citizens of the United States. residing at (1)Hammond and (2) East Chicago. both in the county of Lake and State ofIndiana; and at Boston, in

.the county of Suffolk and Commonwealth of Massachusetts, have inventedcertain new anduseful Improvements in Methods of Making ArsenicalSalts;and we do hereby declare the following to be a full, clear, and exactdescription of the invention, such as will enable others skilled in theart to which it appertains to make and use the same.

The invention relates to the manufacture upon thesulfate. The sulfate ispreferably I in a finely divided state adapted to be held in suspensionin the solution so that it may be thoroughly mixed with and will readilyreact wlth the soluble'arsemcal salt to Eorm a precipitate of thearsenical salt of thc' metal. The mixing of the compounds may beeffected in a dry state before the formation of the solution in whichthe reactions, which result in the production of the arseni; cal salts,take place. but we prefer to mix the compounds by first forming a pulpin which the finely divided sulfate is held in suspension in water, andthen mixing the pulp with a water solution,of the soluble arsenicalsalt, since by this mode of procedure highly satisfactory results havebeen secured.

lVhile the invention may be applied to the production of variousarsenical salts of a number of metals, it is particularly applicable tothe commercial manufacture of lead arscnate or calcium arsenate and willbe specifically described with reference to' the manufacture of thesearsenical salts.

The preferred mode of procedure in producing lead or calcium arsenatefrom the corresponding sulfates in accordance with our invention is asfollows:

The lead or calcium sulfate may be a waste or by-product of some of thechemical in Specification of Letters Yatent. Patgnted ()gt, 26 1926Application .filed June 28, 1919. Serial No. 307,431.

dustries, in which case it may be obtained in a dry form or as a finelydivided chemical precipitate in the form of magma. Calcium sulfate isalso obtainable in its natural state as the mineral gypsum. In case thesulfate to be used is not in a finely divided state, it is ground to afine powder before being subjected to the action of the solublearsenical salt. In the case of lead sulfate obtained as a by-product ofchemical industries and containing soluble impurities, it is preferableto first remove these impurities, as by subjecting the sulfate materialto a preliminary water leaching, filtering and washing process. 1

The finely divided sulfate is mixed with water by stirring agitation orotherwise an til it forms a pulp in which the particles of the sulfateare held insuspension. In the case of lead sulfate, a mixture by weightsof approximately one part of lead sulfate to ten parts of water, and inthe case of calcium sulfate, amixture of approximately one part ofcalcium sulfate to five parts of water has been found to be suitable forour practice, but a wide range of such proportions is permissible. Thispulp is fed slowly and gradually, either intermittently or continuously, by any suitable means, to a solution of a soluble arsenate.W'e preferably use a ten per cent. solution of sodium arsenate in water.Constant stirring agitation of the mixture should be kept up during themixing operation. The conversion of'the insoluble sulfate into thearsenate of the corresponding metal takes place readily. The arsenate oflead or calcium formed is of flocculent character, and therefore remainsreadily in suspension during the agitation. Agitation is preferablycontinued fora short time after all the ingredients have been mixed,which operation is conducive to complete conversion and to theflocculency of the product, I

To insure a complete conversion of the sulfate, we prefer tosubjcct themixture to attrition as well as to agitation, as for instance byagitating the mixture in a porcelain ball mill. any particles of thesulfate which might otherwise be but partially reduced, and

This serves to break up brings all the sulfate into intimate contactwith the soluble arsenate sothat it is completely reduced. While thereactions take place at normal. temperatures, we have found 1t expedientfor conversion of the sulfate attrition as above described.

After completing the reaction, the arsenate precipitate is preferablyleft tosettle' in the reaction mixing tank or mill and the clearsolution is decanted for further treatment for the recovery of anyby-product, such as sodium sulfate, by the evaporation of the excesswater. The residual arsenate magma'is further washed in the usualmanner' to any degree of moisture retaining paste, or the same is driedarid fineround into an arsenate powder if such is esired. The followingreactions are representative of the reactions taking place, showing thecombining ,proportions of the base and arsenate salts of sodium:

Reactions 3 and 6 dilute solutions.

he reactions given above produce the lead arsenate'salts commonly usedas insecticides, or the corresponding calcium arsenate salts, which mayhe used for the same purpose, or for other purposes, or a mixture occurparticularly in too of the normal and acid sodium arsenate salts willresult in a mixture of the two possible arsenate compositions. It may befound desirable to produce either tri or di salt of lead or calciumarsenate, or a mixture of the tri or (ii salts. By using an addition ofa calculated amount of caustic alkali, such as caustic soda, we mayobtain a conversion of the arsenical sodium saltreagent from the di tothe tri salt during the operations described above. In any case theamount of the base (leador calcium) contained in the sulfate should beadjusted to the theoretical combining weights of arsenate in thearsenate solution, although we have found thata slight excess ofthe'arsenate is'beneficial in obtaining the desired results. v

The method described enables lead or calcium araenate to be easily andeconomically produced from material which occurs in nature as a commonmineral or which is pro duced in large quantities as a by-product orwaste product in various processes of the chemical industries. Themethod also on 70 ables the recovery of the soluble sulfate by products,such as sodium sulfate, in case the sodium arsenate is used as thesoluble arsenical salt.

By the use of an arsenite instead of an arsenate as the solublearsenical salt, an arsenite, such for instance as calcium arsenite, may'be produced if found desirable. In such cases, thereactions taking placeupon the mixture of the finely divided sulfate with the solution of thesoluble arsenite, such as sodium arsenite, are indicated as follows:

Other arsenical salts might be secured by variation of the solublearsenieal' salt utilized in the solution with which the finely dividedinsoluble sulfate is mixed.

lVhile the method of procedureoutlined above secures the desired resultsin an efficient and economical manner, it will be understodd that othermodes of procedure may be utilized without departing from the broaderscope of the invention, and that more or less unnecessary andcomplicating steps might be introduced without departing therefrom. Forinstance, the arsenical solution might be added to the sulfate, or thesulfate and soluble arsenical salt might be mixed in a wet or dry stateand then lixiviated with or without agitation to subject the sulfate tothe action of a solution of ar-- senical salt. It will also beunderstood that .105 any manner of agitation, with more or lessmechanical attrition, may be utilized. Other modifications or variationsin the specific mode of procedure in practising the invention maysuggest themselves to persons skilled in the art.

The present application is a continuation in part of a 'iplication.Serial No. 262,700, lilcd Xovcmber '15, 1918.

llaving thus described our-invention, what we claim is: 1

1. The method of making arsenicul salts which consists in converting aninsoluble sulfate of a metal directly into air arscnical salt of themetal by the action thereon of a solution of a soluble arscnical salt.

2. The method of making arsenates which consists in converting aninsoluble sulfate of a metal directly into an arsenatc of the metal byaction thereon of a solution of S0- 25 dium arsenate.

3. The method of making lead arsenates which consists in converting leadsulfate directly into lead arsenate by the action thereon of a solutionof sodium arsenate.

4. T he method of making arsenates which consists in subjecting aninsoluble sulfate of a metal to the action of a solution of a solublearsenieal salt inwhich the sulfate is held in suspension.

5. The method of making arsenical salts which. consists in subjecting awater solution of a soluble arsenical salt in which finely dividedinsoluble sulfate of a, metal is held in suspension to agitation andattrition. e 6. The method of making arsenical salts by the directconversion of an insoluble sulfate of a metal into anarsenical salt ofthe corresponding metal by mixing the sul fate with a soluble arscnicalsalt in a manner to allow the constituents-oi the mixture to react uponeach other.

7. The method of makin; arsena'tes by direct conversion of an insolublesulfate ofa metal into the arsenate ot' the correspondwhich consists inmixing a pulp in which.

lead sulfate is held in suspension in water with a water solution ofsodium arsenate.

10. The method of making arsenates which consists in mixing a pulp inwhich an insoluble sulfate of a metal is held in suspension in waterwith a-water solution of a soluble arsenate and subjecting the mixtureto agitation andattrition.

11. The method of making lead arsenate which consists in mixinga pulp inwhich lead sulfate is held in suspension in water with a water solutionof sodium arsenate and subjecting the mixture to agitation andattrition.

12. The method of making which consists in mixing; a pulp in which aninsoluble sulfate of a metal is held in suspension in water with a watersolution of a soluble arsenate while maintaining the solution. pulp andmixture at a. temperature of between 160 and 212 F. I

'13. The method of makine lead arsenate which consists in mixing a pulpin which lead sulfate is held in suspension in water with a watersolution of sodium arsenate while malntamin the pulp. solution. and

mixture at a temperature oi between 160.

and 212 F."

H. The method of making arsenates which consists in mixing a pulp inwhich an insoluble sulfate of a metal is held in suspension in waterwith a water solution of sodium ars'enate in the presence of causticsoda.

' WILLIAM THUM.

JOHN J. MULLTGAN. HENRY M. SCHLEICI-IER.

a rsenates

